Microsoft's BUILD developer conference is set to take place in San Francisco on April 2nd to April 4th and the devices and services giant is expected to reveal details on the forthcoming Windows 9 operating system. In just 24 hours of opening registration for the event, Microsoft has revealed that the event has sold out.

Microsoft annual BUILD conference is set to happen in April of this year, which is a lot earlier than usual as the previous year's event took place in late October. It's highly likely that Windows 8.1 Update 1 will be shown and maybe even released around this time, introducing new API's and features for both developers and consumers.

Microsoft is also expected to offer details on the forthcoming Windows 9 operating system and seeing as how this event has already sold out, developers are eager to learn more about what Microsoft has up their sleeves. As The Verge notes, we may even see more details on Windows Phone 8.1, the upcoming update for Windows Phone 8 that brings along a notification center and a Siri-like assistant.

Either way, we plan on being at the event in April to bring you all the juicy details, so stay tuned!